Tag data reveal habits of large ocean fish

Satellite information from tags on fish such as blue marlins show how deep the fish dived and where it went. The information helps researchers understand what the fish need to survive in a changing ocean.

It might be one of the longest detailed surveillances ever conducted on a blue marlin, one of the world's premiere gamefish.

Marine artist, conservationist and scientist Guy Harvey, fishing with friends in the waters off his Grand Cayman Island home in November 2009, implanted a 150-pound blue marlin with a pop-up satellite tag. The marlin carried the tag for six months, travelling 3,825 miles before it popped off in May 2010. The small cigar-shaped device transmitted reams of data on the marlin's whereabouts during that time to a satellite.

It will be up to Eric Prince, veteran billfish scientist at NOAA's Southeast Fisheries Science Center in Miami, to analyze the tagging data in more detail, specifically how deep the fish dived and where. Prince has been studying how climate change could direct the movements of large ocean predators such as marlin, other billfish and tuna.

In a new scientific paper published in Nature Climate Change, Prince found that expanding dead zones in the central Atlantic and elsewhere shrinks the habitat for those fish, most of which are already overfished throughout their range. These highly migratory species need large amounts of dissolved oxygen to thrive, but as ocean waters warm and become more acidic, oxygen levels drop. This habitat "squeeze" forces them to make deep dives or swim close to the surface, wherever they can find areas of high dissolved oxygen.